Modern Research in Catalysis, 2013, 2, 57-62
http://dx.doi.org/10.4236/mrc.2013.23009 Published Online July 2013 (http://www.scirp.org/journal/mrc)
Cesium as Alkali Promoter in Me-Cs (Me = Cu, Co, Fe)/
Al2O3 Structured Catalysts for the Simultaneous
Removal of Soot and NOx
Sonia Ascaso, María Elena Gálvez, Rafael Moliner, María Jesús Lázaro
Instituto de Carboquímica, Consejo Superior de Investigaciones Científicas, Miguel Luesma Castán, Zaragoza, Spain
Email: [email protected]
Received January 28, 2013; revised March 3, 2013; accepted April 1, 2013
Copyright © 2013 S. Ascaso et al. This is an open access article distributed under the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
ABSTRACT
Structured catalysts for the simultaneous removal of soot and nitrogen oxides were prepared by means of coating cordierite monoliths with alumina-based suspensions containing Cu, Co or Fe and Cs as the catalytically active phase. Textural and chemical properties of the coated monoliths were determined by means of N2-physisorption, SEM and temperature programmed reduction. Their activity in the simultaneous removal of soot and NOx was assayed in a lab-scale
installation, using a carbon black as diesel surrogate. Catalysts containing Cs exhibited significant activity in deNOx,
however soot oxidation activity is poorly enhanced probably due to the low NO2 evolution, pointing to a different NOx
adsorption mechanism in the present case, in comparison to previous observations on analogous K and Ba containing
catalysts.
Keywords: Exhaust Gas Cleaning; NOx Selective Reduction; Soot Oxidation; Cesium; Washcoating; Structured
Catalysts
1. Introduction
In the last years, diesel vehicles have become leaders in
the automobile market due to their excellent durability.
This trend is expected to continue in the near-term future.
In spite of the fact that diesel engines emit lower amounts
of CO2 and others pollutants, they are important sources
for the emission of particulate matter i.e. soot [1]. Moreover, under typical operating conditions of diesel engines,
i.e. lean-mixtures, three-way catalysts are not efficient in
reducing NOx [2].
The increasing concern about the environmental effects of these contaminants has led to the introduction of
a newer and each time more stringent regulation [3]. The
previously legislative demands have been achieved by
means of implementing engine modifications, such as
common rail technology, the introduction of four valves
per cylinder and exhaust gas recirculation (ERG) cooling
technology. Still, there is always a trade-off between the
reduction of particulate matter emission and nitrogen
oxides control. Thus, in order to meet the upcoming emission standards the use of after-treatment technologies is
strictly required.
In order to reduce the concentration of NOx from autoCopyright © 2013 SciRes.
mobile exhausts under excess oxygen, procedures such
as selective catalytic reduction (SCR) [4,5] and NOx
storage-reduction (NSR) have been previously considered. However, both alternatives suffer from serious difficulties in order to reach its effective implantation. SCR
systems need the presence of a reducing agent, normally
urea, and its corresponding storage and feed units, entailing serious drawbacks to its application in light-duty
vehicles, where space limitations are stricter and fuel
economy is above all sought. NSR catalytic systems still
suffer from serious problems such as low catalytic activity, narrow temperature window of operation and deactivation in the presence of other components in the
exhaust.
The use of a catalyst in combination with particle filter
is one of the most promising after-treatment techniques
to reduce soot emission. An oxidation catalyst decreases
the soot ignition temperature assisting the filter regeneration. NO2 is a powerful soot oxidant, however NO2 concentration in exhaust are normally low (5% - 15% of
total NOx) [6]. The “continuously regenerating trap”
(CRT) technology utilizes a Pt-supported catalyst upstream the particulate filter, allowing partial conversion
MRC
58
S. ASCASO ET AL.
of NO to NO2, which subsequently reacts with the soot
retained in the filter [7-10]. Attempts have been made to
achieve the total reduction of NO2 to N2 simultaneously
to soot oxidation. When using noble metal-based catalytic systems, only partial reduction of NO2 to NO was
reach, with small amounts of NOx totally converted to N2.
On the other hand, some other studies report successful
NOx conversion to N2 [11-16]. In previous works we
reported high activity and selectivity towards N2 and CO2
for several alumina supported catalytic systems containing Cu, Co and V together with K as alkali promoter [17].
In general, in such catalytic systems the alkali promoter,
mainly K, is thought to bring substantial benefits for soot
oxidation, due to the formation of low melting point
compounds, which improve soot-catalyst contact [14,18,
19]. The major drawback of using K is its low stability,
due to the relatively low melting point of its oxide compound, which is responsible for the short durability of the
catalyst. Besides K, Cs based catalysts pose an option,
which has been recently studied as an alternative for soot
oxidation [19-22].
The aim of this work is to prepare and study Al2O3supported Cu, Co or Fe systems, in combination with Cs
as alkali promoter, with the aim of evaluating its activity
in the simultaneous removal of soot and NOx.
2. Experimental
2.1. Catalysts Preparation and Characterization
Cylindrical shaped cordierite monoliths (2MgO·2Al2O3·
5SiO2, Corning, 400 cpsi, 1 × 2.5 cm), were coated using
different suspensions prepared by sol-gel synthesis, using
a highly dispersible boehmite (Disperal, Sasol GmbH).
Such highly dispersible aluminas have been previously
employed as supports [23], in the synthesis of washcoating suspensions [24] or as primers [25], in the preparation of catalysts with similar applications. Cu, Co and Fe
were added to the alumina suspensions (Cu(NO3)2·3H2O,
Co(NO3)2·6H2O or Fe(NO3)3·9H2O) together with Cs
(CsNO3) as alkaline promoter. Metal to promoter mass
ratio was 5:15, for an alumina load of 5% wt., and
HNO3/Al2O3 ratio of 0.1. Mixtures were stirred for 24 hr;
measuring viscosity and pH, after 4 days ageing time.
Coating was performed by forced circulation of the suspensions through the channels of the monoliths, with the
help of a peristaltic pump. After 30 minutes circulation
time, monoliths were dried in a rotating oven at 60˚C
during 24 hours, and subsequently calcined at 450˚C for
4 hours. Table 1 presents a list of the different catalysts
prepared, their labeling, coating suspensions and their
viscosity and pH.
Physico-chemical characterization of the prepared catalysts was performed by means of scanning electron microscopy (SEM, Hitachi S-3400 N), and N2 adsorption at
Copyright © 2013 SciRes.
−196˚C (Micromeritics ASAP 2020), applying BET method for the determination of surface area, BJH and t-plot
methods for the calculation of meso and micropore volume. Catalyst stability, i.e. in terms of loss of alkaline
and alkaline-earth promoter, was evaluated by means of
intensive calcination of the catalyst at 800˚C for 5 hours.
2.2. Activity Tests
Soot filtration was simulated by means of the incorporation of a carbon black (Elftex 430, Cabot, SBET: 80 m2/g,
primary particle mean size: 27 nm), selected due to its
identical behavior upon thermo gravimetric oxidation in
air, vis-à-vis laboratory-produced diesel soot. Still, the
use of a carbon black can be considered as a conservative
experimental approach, since the presence of soluble
organic fraction (SOF) in real soot contributes to increased reactivity [26]. Each catalyst was introduced for
1 min into a continuously stirred dispersion of 0.2 g of
carbon black in 100 mL n-pentane, and then dried at
65˚C during 1 hour. Weighting the catalysts before and
after allows the determination of the amount of carbon
black loaded, which corresponded to approx. 20% wt.
with respect to the mass of catalytic material deposited
on the surface of the monolith.
The activity of the prepared catalysts in the simultaneous removal of soot and NOx was assayed in a labscale fixed bed installation. A reactant gas containing
500 ppmv NO and 5% O2 in Ar was flowed at 50
mL/min through a catalyst (1 × 2.5 cm). Experiments
were performed at temperatures between 250˚C and
650˚C, heating rate of 5˚C/min. Concentrations of the
different compounds were analyzed by means of mass
spectrometry (Balzers 422) and gas chromatography
(Varian Micro GC CP 4900). NO conversion, X NO , and,
X NOx were calculated from the molar concentrations:
i
X NO  mNO mNO
. Carbon black conversion, X CB , was
calculated using the initial amount of carbon black and
the molar concentrations of CO and CO2:
i
X CB  mCO2  mCO mCB
. CO and CO2 concentrations
were determined by means of GC. NO, NO2 and N2 concentrations were calculated from the data registered by
the MS, taking into account the possible contributions of
the rest of the components to their corresponding princepal m/z values of 30, 46 and 28. N2O formation was assessed by comparison of concentration of CO2 measured
by GC and concentration obtained from m/z 44 in MS.


3. Results and Discussion
3.1. Catalysts Characterization
As previously discussed elsewhere [27,28], viscosity and
pH of the suspensions, see Table 1, depend upon their
composition. In this case, the use of Co results in less
MRC
S. ASCASO ET AL.
59
10.1 m2/g, higher than in the originally macro-porous
cordierite, pointing to pore filling upon coating. In fact,
pore volume corresponds mostly to mesopores, with values ranging from 0.017 to 0.021 cm3/g, and average pore
sizes from 7.0 to 7.6 nm.
viscous suspensions. In all cases suspensions show stabilization pH values lower than the one corresponding to
alumina isoelectric point [around 3 - 4], pointing to incomplete H+ consumption. In general, the use of Cs as
promoter results in a somehow more complicated gelation process, yielding suspensions of lower viscosity and
pH with respect to previous observations using K and Ba
[29]. This fact can be ascribed to its higher ionic size in
comparison to K and Ba [30]. In spite of the differences
among the properties of these suspensions, coating of the
cordierite monoliths results in similar amounts of catalytic material loaded, 10% weight on average, see Table
1. Uniform coating was observed in all cases; see Figure
1 which presents SEM images acquired for FeK, FeBa
and FeCs catalysts. Table 1 shows as well average layer
thickness measured by means of SEM inspection of the
cross section of the coated monoliths, see as well Figures 1(d)-(f).
Table 2 shows the results obtained in the textural characterization of the catalysts by means of N2 adsorption.
The catalysts exhibit surface areas, SBET, between 8.8 and
3.2. Catalytic Activity
Figure 2 shows the results obtained in the simultaneous
removal experiments for FeCs, CuCs and CoCs catalysts.
Figures 2(a), (c) and (e) show the evolution of N-species,
i.e. (1-XNO), N2 and NO2 concentration, together with XCB;
Figures 2(b), (d), and (f) represent the evolution of CO and
CO2 in the experiments as well as XCB. In all the catalyst,
an initial N-species adsorption stage can be observed, taking
place at temperatures from 250˚C to 400˚C, see Figure 2(a),
(c) and (e). No N2 evolution was evidenced, fact that allows
ascribing the observed reduction in the concentration of NO
to its adsorption on the catalyst surface, almost neglecting the contribution of selective reduction of NOx during this period. This adsorption stage is immediately
followed by the desorption of N-species, mainly as
Table 1. Catalyst labeling, suspension viscosity at shear rate 1 s−1 and pH after 4 days ageing time, weight increase upon
monolith coating and average thickness of the deposited catalytic layer.
Catalyst
Viscosity (mPa·s)
pH
% weight increase after coating
Average layer thickness (m)
CuCs
2046
1.7
10.2
29
CoCs
1869
1.7
9.8
25
FeCs
3190
1.3
9.9
20
(a)
(b)
(c)
(c)
(d)
(e)
Figure 1. SEM images acquired for (a) and (d) CoCs, (b) and (e) CuCs, and (c) and (f) FeCs catalysts. Note: images (d), (e)
and (f) correspond to cross sectional view of the catalysts, tangential to gas flow.
Copyright © 2013 SciRes.
MRC
S. ASCASO ET AL.
1000
0.6
750
i
1-XNO = mNO/mNO
XCB
500
NO2 concentration (MS)
N2 concentration (MS-GC)
300
400
500
Temperature (˚C)
0
600
2.0
XCB (GC)
CO concentration (GC)
1.0
750
XCB = 1
500
250
0.5
0.0
300
400
1-XNO and XCB (-)
0.8
1000
i
1-XNO = mNO/mNO
XCB
NO2 concentration (MS)
750
N2 concentration (MS-GC)
500
0.2
250
0.0
300
400
500
0
600
XCB (-) and CO2 concentration (%)
1250
NO2 and N2 Concentration (ppm)
XNO = 0
0.4
2.5
2.0
Temperature (˚C)
XCB (GC)
1.0
CO concentration (GC)
0.0
3.0
0.6
750
i
1-XNO = mNO/mNO
XCB
500
NO2 concentration (MS)
N2 concentration (MS-GC)
300
400
250
500
0
600
XCB (-) and CO2 concentration (%)
1000
NO2 and N2 Concentration (ppm)
1-XNO and XCB (-)
0.8
0.0
1000
750
XCB = 1
500
250
0.5
1500
1250
0.2
1250
CO2 concentration (GC)
300
400
500
Temperature (˚C)
600
0
(d)
XNO = 0
0.4
0
1500
XCB (MS)
(c)
1.0
600
1.5
Temperature (˚C)
500
(b)
3.0
1500
0.6
1000
1.5
(a)
1.0
1250
CO2 concentration (GC)
CO concentration (ppm)
0.0
250
2.5
1500
XCB (MS)
2.5
2.0
1500
XCB (MS)
XCB (GC)
1250
CO2 concentration (GC)
CO concentration (GC)
1000
750
1.5
1.0
XCB = 1
500
250
0.5
0.0
300
400
500
Temperature (˚C)
Temperature篊
(˚C)
(e)
(f)
600
CO concentration (ppm)
0.2
XCB (-) and CO2 concentration (%)
1-XNO and XCB (-)
0.8
NO2 and N2 Concentration (ppm)
1250
0.4
3.0
1500
XNO = 0
1.0
CO concentration (ppm)
60
0
Figure 2. Simultaneous carbon black and NOx removal experiments in the presence of the catalysts FeCs, (a) and (b); CuCs,
(c) and (d) and CoCs (e) and (f).
Table 2. Textural characterization, surface area, SBET,
mesopore volume, Vmeso, and average pore size, for the different catalysts prepared.
Catalyst
SBET (m2/g)
Vmeso (cm3/g)
Average pore
size (nm)
CuCs
9.7
0.021
7.4
CoCs
8.8
0.017
7.0
FeCs
10.1
0.021
7.6
Copyright © 2013 SciRes.
NO. Only in the case of CuCs, Figure 2(c), NO2 evolution can be clearly observed. This fact points out principal to different adsorption mechanism taking place when
using Cs as alkali promoter in comparison to preferable
NO2 desorption observed for K containing catalyst [27].
At 450˚C carbon black oxidation sets off. In the same
temperature window, 500˚C - 600˚C N-species are simultaneously reduced. NO conversion peaks at around
525˚C in all the cases, reaching XNO = 0.55 for FeCs
catalyst, XNO = 0.42 for CoCs catalyst whereas in the
MRC
S. ASCASO ET AL.
case of CuCs, lower NO conversion was measured, XNO
= 0.32.
With respect to carbon black conversion, XCB, Figures
2(b), (d) and (f) show evidence that it is partially non
selective towards CO2 in the lower temperature interval
from 450˚C to 550˚C, as indicated by the measured CO
evolution. At higher temperature, however CO2 production prevails and almost no CO can be further measured.
Maximal carbon black conversion reached at 650˚C, is
similar using FeCs and CoCs, XCB = 0.40, and lower for
CuCs, XCB = 0.30.
In comparison to previous results obtained using K
and Ba as alkali promoters [29] carbon black conversion
is all the times lower in the presence of Cs-containing
catalysts, moreover when compared to K-containing ones.
This observation can be possible ascribed to different
nitrogen species adsorption mechanism. When using Kcontaining catalysts NO2 concentrations reached 1200
ppm. Preferable NO2 evolution measured in the case of
K-catalyst may result in enhanced carbon black oxidation,
as previously reported in the existing literature [31].
http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=
OJ:L:2007:171:0001:0016:EN:PDF
[4]
A. Boyano, M. J. Lázaro, C. Cristiani, F. J. MaldonadoHodar, P. Forzatti and R. Moliner, “A Comparative Study
of V2O5/AC and V2O5/Al2O3 Catalysts for the Selective
Catalytic Reduction of NO by NH3,” Chemical Engineering Journal, Vol. 149, No. 1-3, 2009, pp. 149-173.
doi:10.1016/j.cej.2008.10.022
[5]
A. Boyano, N. Lombardo, M. E. Gálvez, M. J. Lázaro and
R. Moliner, “Vanadium-Loaded Carbon-Based Monoliths
for the On-Board NO Reduction: Experimental Study of
Operating Conditions,” Chemical Engineering Journal,
Vol. 144, No. 3, 2008, pp. 343-351.
doi:10.1016/j.cej.2008.01.037
[6]
I. P. Kandylas, O. A. Haralampous and G. Koltsakis, “Diesel Soot Oxidation with NO2: Engine Experiments and
Simulations,” Industrial and Engineering Chemistry Research, Vol. 41, No. 22, 2002, pp. 5372-5384.
[7]
S. Matsumoto. “Recent Advances in Automobile Exhaust
Catalysts,” Catalysis Today, Vol. 90, No. 3-4, 2004, pp.
183-190. doi:10.1016/j.cattod.2004.04.048
[8]
A. Setiabudi, B. A. A. L. van Setten, M. Makkee and J. A.
Moulijn, “The Influence of NOx on Soot Oxidation Rate:
Molten Salt versus Platinum,” Applied Catalysis B: Environmental, Vol. 35, No. 3, 2002, pp. 159-166.
doi:10.1016/S0926-3373(01)00251-X
[9]
O. Salvat, P. Marez and G. Belot, “Passenger Car Serial
Application of a Particulate Filter System on a Common
Rail Direct Injection Diesel Engine,” SAE Technical
Paper 2000-01-0473, 2000.
4. Conclusions
Structured catalysts were prepared by means of coating
cordierite monoliths with alumina-based suspensions containing transition metals (Cu, Co, Fe) and Cs as alkali
promoter. Their activity was assayed in the simultaneous
removal of soot and NOx.
Coating led to the deposition of a catalytic layer of 20 29 m average thickness. After coating, surface areas of
the monoliths increased as a consequence of the deposition of the catalytic layer, which was mostly mesoporous
and filled the macroporous structure of the original cordierite material.
Catalysts exhibited considerable deNOx activity, reaching 55% conversion. The use of Cs as alkali promoter
gave rise to low NO2 evolution, resulting in lower activity towards soot oxidation for this system in comparison
with previously studied K-containing catalyst. This fact
may be assigned to different N-species adsorption mechanisms taking place in the presence of Cs, which must
be further studied in detail.
REFERENCES
[1]
[2]
[3]
R. J. Farrauto and K. E. Voss, “Monolithic Diesel Oxidation Catalysts,” Applied Catalysis B: Environmental, Vol.
10, No. 1-3, 1996, pp. 29-51.
doi:10.1016/0926-3373(96)00022-7
P. Ciambellia, P. Corbob and F. Migliardinib, “Potentialities and Limitations of Lean De-NOx Catalysts in Reducing Automotive Exhaust Emissions,” Catalysis Today,
Vol. 59, No. 3-4, 2000, pp. 279-286.
doi:10.1016/S0920-5861(00)00294-7
European Regulation, “Regulation EC N. 715/2007”.
Copyright © 2013 SciRes.
61
[10] B. R. Stanmore, J. F. Brihlac and P. Gilot, “The Oxidation of Soot: A Review of Experiments, Mechanisms and
Models,” Carbon, Vol. 39, No. 15, 2001, pp. 2247-2268.
doi:10.1016/S0008-6223(01)00109-9
[11] K. Hizbul, S. Kureti and W. Weisweiler, “Potassium ProMoted Iron Oxide Catalysts for Simultaneous Catalytic
Removal of Nitrogen Oxides and Soot from Diesel Exhaust Gas,” Catalysis Today, Vol. 93-95, 2004, pp. 839843. doi:10.1016/j.cattod.2004.06.094
[12] N. Neja and M. J. Illán-Gómez, “Potassium-Copper and
Potassium-Cobalt Catalysts Supported on Alumina for Simultaneous NOx and Soot Removal from Simulated Diesel Engine Exhaust,” Applied Catalysis B: Environmental,
Vol. 70, No. 1-4, 2007, pp. 261-226.
doi:10.1016/j.apcatb.2006.03.026
[13] D. Fino, P. Fino, G. Saracco and V. Specchia, “Studies on
Kinetics and Reactions Mechanism of La2−xKxCu1−yVyO4
Layered Perovskites for the Combined Removal of Diesel
Particulate and NOx,” Applied Catalysis B: Environmental, Vol. 43, No. 3, 2003, pp. 243-259.
doi:10.1016/S0926-3373(02)00311-9
[14] V. G. Milt, E. D. Banús, M. A. Ulla and E. E. Miró, “Soot
Combustion and NOx Adsorption on Co,Ba,K/ZrO2,” Catalysis Today, Vol. 133-135, 2008, pp. 435-440.
doi:10.1016/j.cattod.2007.11.013
[15] H. Lin, Y. Li, W. Shangguan and Z. Huang, “Soot OxidaTion and NOx Reduction over BaAl2O4 Catalyst,” Combustion Flame, Vol. 156, No. 11, 2009, pp. 2063-2070.
doi:10.1016/j.combustflame.2009.08.006
MRC
62
S. ASCASO ET AL.
[16] W. F. Shangguan, Y. Teraoka and S. Kagawa, “Promotion Effect of Potassium on the Catalytic Property of
CuFe2O4 for the Simultaneous Removal of NO(x) and
Diesel Soot Particulate,” Applied Catalysis B: Environmental, Vol. 16, No. 2, 1998, pp. 149-154.
doi:10.1016/S0926-3373(97)00068-4
[17] M. E. Gálvez, S. Ascaso, R. Moliner and M. J. Lázaro.
“Me (Cu, Co, V)-K/Al2O3 Supported Catalysts for the
Simultaneous Removal of Soot and Nitrogen Oxides from
Diesel Exhausts,” Chemical Engineering Science, Vol. 87,
2013, pp. 75-90. doi:10.1016/j.ces.2012.10.001
[18] R. Matarrese, L. Castoldi, L. Lietti and P. Forzatti, “Soot
Combustion: Reactivity of Alkaline and Alkaline Earth
Metal Oxides in Full Contact with Soot,” Catalysis Today,
Vol. 136, No. 1-2, 2008, pp. 11-17.
doi:10.1016/j.cattod.2008.03.022
[19] L. Castoldi, R. Matarrese, L. Lietti and P. Forzatti, “Intrinsic Reactivity of Alkaline and Alkaline-Earth Metal
Oxide Catalysts for Oxidation of Soot,” Applied Catalysis
B: Environmental, Vol. 90, No. 1-2, 2009, pp. 278-285.
doi:10.1016/j.apcatb.2009.03.022
[20] A. Setiabudi, N. K. Allaart, M. Makkee and J. A. Moulijn,
“In Situ Visible Microscopic Study of Molten Cs2SO4•V2O5Soot System: Physical Interaction, Oxidation Rate, and
Data Evaluation,” Applied Catalysis B: Environmental,
Vol. 60, No. 3-4, 2005, pp. 233-243.
doi:10.1016/j.apcatb.2005.03.005
[21] A. Aissat, S. Siffert and D. Courcot, “Investigation of CsCu/ZrO2 Systems for Simultaneous NOx Reduction and
Carbonaceous Particles Oxidation,” Catalysis Today, Vol.
191, No. 1, 2012, pp. 90-95.
doi:10.1016/j.cattod.2012.01.020
[22] N. F. Galdeano, A. L. Carrascull, M. I. Ponzi, I. D. Lick
and E. N. Ponzi, “Catalytic Combustion of Particulate
Matter: Catalysts of Alkaline Nitrates Supported on Hydrous Zirconium,” Thermochimica Acta, Vol. 421, No.
1-2, 2004, pp. 117-121. doi:10.1016/j.tca.2004.04.006
[23] M. Boutros, J.-M. Trichard and P. Da Costa, “Effect of
the Synthesis Method on Alumina Supported Silver
Based Catalyst for NOx Selective Reduction by Ethanol,”
Topics in Catalysis, Vol. 52, No. 13-20, 2009, pp. 17811785. doi:10.1007/s11244-009-9335-9
Copyright © 2013 SciRes.
[24] C. Cristiani, A. Grossale and P. Forzatti, “Study of the
Physico-Chemical Characteristics and Rheological Behaviour of Boehmite Dispersions for Dip-Coating Applications,” Topics in Catalysis, Vol. 42-43, No. 1-4, 2007,
pp. 455-459. doi:10.1007/s11244-007-0224-9
[25] N. R. Peela, A. Muyabi and D. Kunzru, “Washcoating of
γ-Alumina on Stainless Steel Microchannels,” Catalysis
Today, Vol. 147, 2009, pp. S17-S23.
doi:10.1016/j.cattod.2009.07.026
[26] F. Bonnefoy, P. Gilot, B. R. Stanmore and G. Prado, “A
Comparative Study of Carbon Black and Diesel Soot Reactivity in the Temperature Range 500 - 600˚C -effect of
additives,” Carbon, Vol. 32, No. 7, 1994, pp. 1333-1340.
doi:10.1016/0008-6223(94)90120-1
[27] M. E. Gálvez, S. Ascaso, R. Moliner, R. Jiménez, X.
García, A. Gordon and M. J. Lázaro, “Catalytic Filters for
the Simultaneous Removal of Soot and NOx: Effect of
CO2 and Steam on the Exhaust Gas of Diesel Engines,”
Catalysis Today, Vol. 176, No. 1, 2011, pp. 134-138.
doi:10.1016/j.cattod.2011.01.030
[28] M. E. Gálvez, S. Ascaso, I. Tobías, R. Moliner and M. J.
Lázaro, “Catalytic Filters for the Simultaneous Removal
of Soot and NOx: Influence of the Alumina Precursor on
Monolith Washcoating and Catalytic Activity,” Catalysis
Today, Vol. 191, No. 1, 2012, pp. 96-105.
doi:10.1016/j.cattod.2011.12.012
[29] M. E. Gálvez, S. Ascaso, R. Moliner and M. J. Lázaro,
“Influence of the Alkali Promoter on the Activity and
Stability of Transition Metal (Cu, Co, Fe) Based Structured Catalysts for the Simultaneous Removal of Soot and
NOx,” Topic in Catalysis, in Press.
[30] M. Colic, G. V. Franks, M. L. Fisher and F. F. Lange,
“Effect of Counterion Size on Short Range Repulsive
Forces at High Ionic Strengths,” Langmuir, Vol. 13, No. 12,
1997, pp. 3129-3135. doi:10.1021/la960965p
[31] B. R. Stanmore, V. Tschamber and J. F. Brilhac, “Oxidation of Carbon by NOx, with Particular Reference to NO2
and N2O,” Fuel, Vol. 87, No. 2, 2008, pp. 131-146.
doi:10.1016/j.fuel.2007.04.012
MRC